Transcript riverfeatures

3. River Profiles and Processes
WALT
To understand the 3 main courses of a
river and their characteristics.
Understand the main processes which
happen in each stage.
GENERAL CHARACTERISTICS
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• A river LONG PROFILE is a sideways look at a
river valley from source to mouth.
• It can also be called a LONG SECTION.
• In an ideal river, it looks like this;-
• The key to understanding how a river creates its
landforms is to look at the energy needed to move
the material around it.
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• Large sized material needs high energy.
• Large amounts of material needs high energy.
• Tiny particles need only low amounts of energy.
• Small amounts of material need little energy.
Which
Which
Which
Which
course
course
course
course
has has
Vhas
has
– the
shaped
the
the
steepest
most
fastest
valleys/
erosion?
slope?
flow?
waterfalls/
meanders/ ox-bow lakes/ floodplains
Upper Course
Middle Course
Lower Course
Steep Slope
Moderate Slope
Gentle Slope
Fast Flow
Moderate Flow
Slow Flow
Erosion
Transportation
Deposition
transportation
V-shaped Valley
Waterfall
Gorge
deposition
Small Meander
transportation
Large Meander
Small Floodplain Large Floodplain
Ox-Bow Lake
Methods of Transportation
1. Traction: The force of water rolls and drags the
larger particles long the bed of the river.
2. Saltation: particles bounce along the river bed.
3. Suspension: Finest particles (clay and silt) are
carried in suspension, being swirled along by the
water.
4. Solution: The river transports the products of
chemical weathering from the hillsides and river
bed.
4. River features
WALT
• To understand what features are found
in each stage of a river
• And be able to describe their
formation.
Formation of a water fall
(Upper course)
1. Describe simply the
rock-type layout of a
typical waterfall.
2. Describe where and
how the plunge pool is
created.
3. Why does the
rock layer
collapse?
4. What twoword landform is
created by these
processes?
5. Name and locate
two examples of
this feature.
Formation of a waterfall
ANSWERS
1.A layer of
hard rock lies
over softer rock.
2.The plunge
pool is created
by water eroding
vertically and
laterally below
the hard rock.
3. The rock layer
collapses as a result of
the weight of the hard
rock and gravity.
4.This creates a river
gorge.
5.Thornton Force on the
River Twiss, Ingleton.
High Force on the River
Tees.(examples only! )
Note this
is a river
gorge !
Can you fit these terms together
with an annotated diagram?
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Paragraph 1
Upper course
River – hard rock to soft rock
Rocks different hardness erode different rates
Soft erodes quickly hard slowly
Soft downstream hard rock upstream
Explain erosion for marks
Differential erosion
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Paragraph 2
Soft rock erodes - steep section - waterfall
Base – plunge pool develops
Water swirls rocks in pool – soft erodes back further
Hard rock undercut – overhangs – collapses
Process repeats moving upstream
Paragraph 3
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Stage retreat
Narrow – steep sided valley - gorge
Formation of a V Shaped Valley
4 The eroded material that falls into
3 As
the rock & soil from the river
the river is then
transported
breaks
downstream by bank
the river
andup,
is it is transported to
bybeach.
to gravity and the
deposited on its bed orthe
on river
a river
wash effect of rain on the soil.
1 As the river flows it erodes
downwards initially (vertical erosion),
due to the great energy it has. This
happens mainly because of the process
of corrasion (explain in detail for in
2 The river therefore forms a deep
exam!)
and steep sided channel. Over time
freeze thaw (again explain)
weathering acts upon the riverbank.
This loosens the rock and soil.
Middle course: Meanders
• These are found initially in the middle
stage, although they get well
developed in the lower stage too.
SINUOSITY
WAVELENGTH
POINTS OF
INFLEXION
The first stages in the formation of
meanders is believed to be the
development of ‘riffles and pools’.
These are zones of
alternating deposition
and erosion that
cause the channel of
the river to alter
course, thus creating
the meander.
Meander
Remember that
meanders are a
developing feature,
changing with time and
moving both across the
flood plain and downstream!
Remind yourself how
they do this- what are
the PROCESSES?
Notice how the
inner bank is
being built up into
a point bar
deposit /river
beach/ slip-off
slope, and the
outer bank is
being eroded into
a river cliff.
The photograph here and
the diagram on the next
slide shows the processes
going on below the water.
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Now sequence an answer
explaining this process
Pool
River Beach
Riffle
River Cliff
water ~ river ~ flows ~ pool to riffles ~ pool ~ deep slow ~ riffle ~ shallow
fast ~ causes ~ movement ~ water ~ side ~ side ~ development ~ meander
Inner Bend
Slow Flow – Low Energy
Outer Bend
Fast Slow – High Energy
Small Rocks
Large Rocks
Deposition - Sediment
Erosion - Corrasion
Shallower Channel
Deeper Channel
Builds Up Bank
Undercuts Bank
River Beach
River Cliff
Formation of an ox bow lake
A
The finale of the
process is for an
ox-bow lake to
form.
B
An ox-bow lake on the Endrick
valley floodplain.
The meanders
and ox-bow
lakes of the
Mississippi
River from the
air.
The movement of the meanders create
the wide floodplain and bluffs of the
mature lower stage of the river.
Lower Stage
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The gradient is lower
Energy levels are low
Much deposition
High sinuosity
Floodplain is wide
Levees
• Levees are either natural or manmade raised banks.
Reducing Impact of flooding
Braiding
• Use the textbook to help you answer
these questions
1.Why are there
sometimes greater than
usual amounts of load in
the channel?
2. What causes this
load to be deposited?
3. Explain why
these mounds of
material are
unstable?
1. Increased discharge in
the river will bring down
more (and larger) load from
upstream.
2. If the discharge drops
quickly, reducing the volume
in the channel, the material
will be dropped in the bed.
3. The material is poorly
consolidated and is likely to
be re-eroded with further
increased discharge.
Sometimes debris
remains long
enough to be
colonised with
vegetation which
stabilises it more!
Deltas
Answer these DELTA questions;1.Why does a delta
not form if there are
tides or currents?
2. Why are the beds/
sets graded by size?
3. Why do
distributaries form?
flow
1. Currents would wash away the deposits before they
could gather.
2. As the material reaches the still water, the river
flow almost stops. The heavier material drops and rolls
down the slope offshore, and the medium particles fall
on top of them. The lightest particles are carried
further out to sea and deposited, to be covered much
later by more heavy deposits.
3. Distributaries form as the water has trouble flowing
over the deposited material.
Floodplain
Flood
= When a river bursts its banks.
Plain
= Flat area of land.
Floodplain = The flat area of land either side of a river, which often floods.
Now draw a diagram showing what a floodplain
looks like and how it develops
Bluff line
Explaining Floodplain Development
flood water – contact  land area – friction – slower flow – deposition;
repetition of flooding – layers – sediment – build up – flatter; flat land –
flat
– bystones
river –
flood;
heavy rain –– snow
- – discharge
largest
– first
– embankment
parallelmelt
– river
levee; water–
– line;
banksediment
bursts; –energy
– –river
rocks; – water –
valley sideriver
– bluff
build up
river–channel
spreads – loses more energy – medium stones; further friction –
higher – land – enclosed by levees – prone to flood;
smallest stones – valley sides;
These are flat areas of land either side of a river, which are prone to flooding ().
During periods of heavy rain and or snow melt () river discharge will increase to
a point whereby it bursts its banks (). The river has a lot of energy at this point
and so carries many rocks () and sediment.
When the flood water leaves the river channel it comes in contact with a greater
land surface () and so friction between the water and land increases (), which
reduces the speed of the river causing deposition (). With this initial slowing of
the water the largest stones are deposited forming a small (natural) embankment
() parallel with the river called a levee (). As the flood water continues to
spread to the valley sides it loses even more energy depositing medium sized
stones () and eventually with as it slows to a stop the smallest deposits are
dropped near the valley side ().
Every time there is a flood the same process happens, meaning layer upon layer
of sediment builds up making the land flatter (). The point where this flat area
meets the steeper valley side is caused the bluff line ().
The likelihood of the river flooding is increased if a lot of sediment has been
deposited in the river channel () over a period of time. This means that the river
can be at a higher level than the land (), being enclosed by the levee’s, and so
will be more prone to flooding ().